I took the time to look at your linked website. From a photographic point of view I believe you will really like the lens and it certainly has the potential to take you to higher levels, the focal length is longer than most of your people shots and this gives not only a different look but a different dynamic to the shoot, I have always found giving the subject more room to be better. Having said that, with your loose style, I believe you would really get the use out of IS and would suggest a secondhand MkI IS over a new non IS. Of course you don't need one to get better and in and of itself, especially on web sized images, your output won't look much different, but using one can give your shooting style a kick.